In foundries, metal is poured into molds which are fabricated from special mixes of sand and special-purpose bond/adhesive compositions. This invention addresses apparatus and methods for making, using, and recycling the sand mix. The invention specifically addresses use of particulate bond materials which remain in particulate form when mixed with water, and apparatus and methods for controlling dust which may be generated in the process of making and using such sand mixes.
In making the sand mix, sand is mixed with water, and with the bond material. The bond material is a finely-powdered mixture of e.g. bentonite clay, coal, and a combination of compatibilizers, stabilizers, wetting agents, and the like.
In conventional sand preparation, the sand mix is generally made up in a mullor. In general, a mullor is a special purpose mixing tank. Sand and bond material are metered into the mullor at specified ratios or rates. Water is added to the tank in defined quantity. A typical charge to the mullor is comprised primarily of return sand, with make-up quantities of fresh bond material and fresh sand, in combination with sufficient water to bring the resultant water content of the mix to the desired level.
A mix motor or the like rotates mixing paddles and/or wheels inside the mullor to mix the respective components placed therein. The mixing of sand in the mullor can be either a batch process or a continuous stream process. The exiting sand is preferably tested against a standard, and adjustments to the dry or wet ingredients currently in the mullor are made in response to results of those tests of completed product which have recently exited the mullor.
Typical bond material is a finely powdered particulate material, so fine as to easily become airborne as dust in a gaseous environment such as the air inside the mullor. Such particulate bond material is in general smaller than 200 mesh, and is typically added to the mullor in dry form, and thus is susceptible to becoming air borne until such time as the respective particles become wetted with the water. Indeed, that wetting process is part of the function of the mulling operation. In general, the mullor should accomplish the tasks of uniformly dispersing the fresh sand and fresh bond material, and substantially wetting all bond and sand particles.
In general, the sand particles tend to be relatively hydrophilic while the bond material particles tend to be relatively hydrophobic. Thus, the water tends to be more attracted to the relatively larger sand particles than to the relatively smaller bond material particles whereby the relative tendency for wetting sand particles with a given batch of water is greater than the relative tendency for wetting bond particles with the respective batch of water. Namely, absent an excess of water, the water is selective in tending to wet sand surfaces more readily than bond material surfaces, thereby running the risk that a significant fraction of the bond particles may not be wetted. Accordingly, one of the objects of this invention is to increase the fraction of the fresh bond particles which are effectively wetted by the water.
Typically, freshly-added bond material is fed into the mullor as a stream of dry particles, e.g. transported pneumatically or dropped by gravity into the mullor receptacle. As the dry particulate bond material enters the mullor receptacle in the conventional manner, a fraction of the bond material can and does become entrained in the air through which the bond material passes as the bond material drops to either the bottom of the tank or to a mass of sand, water, and/or other bond material already in the tank. In addition, to the extent bond material lands on underlying dry material already in the mullor, e.g. relatively dry return sand or previously added and still-dry bond material, the dropping dry bond material particles land on the bond material particles on the surface of such underlying material are free to become air-borne upon sufficient agitation or other disturbance, whether solid, liquid, or gaseous agitation. Indeed, so long as such small particles are not wetted, the particles readily go air-borne upon even mild agitation, much like edible grain flours.
Accordingly, one of the primary sources of dust in foundry operations is dry, or relatively dry, particulate bond material in the sand system. A first mechanism for such dust to become air-borne is bond material which becomes dispersed in the air inside the mullor as the bond material is added to the mullor, and as the bond material is in general being mixed with the sand and water. Since bond material, sand, and water are repeatedly or constantly being added to the mullor, and discharged from the mullor, there is an ongoing flow of air into the mullor, and out of the mullor. If no controls are placed on flow of such air, much of the air which exits the mullor will pass to ambient, and will carry with it substantial quantities of air-borne particulate bond material pollution.
Accordingly, it is well known to provide dust collection apparatus as part of a sand system, for capturing particulate material which becomes entrained in the air in the mullor and in other parts of the sand system. Indeed, typical foundry sand systems generate waste particulate bond material amounting to about 25 percent to about 50 percent by weight of the particulate make-up bond material fed to such sand systems, as it is common that such quantity is eventually collected in the dust collection system.
In addition to providing for addition of make-up quantities of bond material, provisions are also conventionally made for addition of make-up quantities of sand. Sand can be lost e.g. as dust. However, the usefulness of the sand is degraded with use. Accordingly, there is a need to routinely and regularly remove used sand from the sand system and to replace such used sand with fresh sand, or regenerated sand. As used herein, xe2x80x9cregenerated sandxe2x80x9d refers to sand which has been removed from the sand system use cycle, and which has been regenerated by e.g. washing, removal of non-sand materials, sizing, and the like.
It is common for the sand system to be operated on a positive replacement basis, wherein sand is routinely removed from the system, and replaced by adding sand at e.g. the sand mixing stage of the sand system. While sand can be selected for removal according to a number of factors, it is common to pass the sand through sizing screens at the work stations where the sand molds are broken away from the cast metal parts, and to remove any chunks of sand which do not pass through the sizing screens. In addition, it is common to deposit the return sand in one or more surge tanks, and to remove from the system any sand which accumulates in the surge tanks above a pre-set volume level.
Such accumulation can occur, for example, where the sand mix prepared at the sand mixing station contains a first pre-determined fraction of return sand and a second pre-determined fraction of fresh make-up sand. Where the quantity of the fresh make-up sand is greater than the quantity of sand lost in use of the sand system, the overall quantity of sand in the sand system potentially increases by the difference. It is such difference which represents the quantity of sand which is removed from the surge tanks, thereby to balance the quantity of sand leaving the sand system with the quantity of sand entering the sand system at the sand mix process.
A second locus for generation of such air-borne bond material, e.g. as dust, is in the sand return system, especially at the entrance to the sand return system.
In general, material so collected in a dust collection system which is connected to a such sand system cannot be economically recycled into the sand system, and is thus sent to land fill as waste. Such waste adds to the cost of the process, in that (i) bond material purchased for the purpose of making sand mix is sent to land fill either prematurely before utility of such bond material is exhausted, or without ever being used at all as part of the sand mix; and in that (ii) the cost of the land filling operation is greater than a minimum threshhold amount theoretically required by foundry operations.
In addition, bond material which is not wetted, and wherein bonding properties are accordingly not activated by the water, but which is nonetheless captured as trapped particles in the sand mix, in inactive and thus does not act in a bonding capacity in the sand mix, and thus can become inadvertently separated from the sand mix during mold casting and cooling. Such separation of bond material particles from the sand mix can leave voids and cavities in the mold, which enable development of inconsistencies in the metal parts molded using such molds. Such inconsistencies can affect the qualities, including strength properties, of sand molds made with such sand mix, and can correspondingly affect the ranges of various properties of metal parts in a population of such metal parts cast in molds made with such sand mix.
Known dust collection systems are capable of capturing substantial fractions of the dust so generated. However, as with all known dust collection systems, the cost of collecting the dust increases greatly as one increases the required fraction of the dust which is to be collected. Unless extreme measures are taken to collect absolutely all dust, and such measures are usually prohibitively expensive, some fraction of the dust always eludes collection and thus makes an incremental contribution to ongoing particulate pollution of the ambient air and thereby has a deleterious affect on air quality.
Since air pollution standards generally address absolute quantities of pollutants emitted, not fractions of the quantity of pollutant generated by the process of interest, when the quantity of particulates generated increases, the amount of collection effort required increases by a like amount, typically according to an asymptotic curve. Conversely, where the quantity of particulates generated is reduced, the amount of collection effort required can decrease by a like amount. Thus, there is an ongoing social and political incentive to reduce the quantity of particulate material which is released into ambient air. There is a corresponding financial incentive for the operator of such foundry to reduce the quantity of particulate material which is produced, and which must thus be controlled and/or captured as a result of the sand system and process.
In foundry systems of interest in this invention, the primary sources of the dust of interest are the bond material which is not wetted or otherwise captured by the water or the wetted sand, and bond material which is released at or after mold breakage.
Bond material particles which become wetted by water correspondingly have taken on increased weight of the water and are thus larger and more dense, whereby an increased level of energy is required to make such particles air borne. In addition, such wetted particles develop adhesive properties as a result of such wetting, which also serve to inhibit the particles becoming or remaining air borne when such particles are in contact with each other or with e.g. respective sand particles.
The inventor herein contemplates that the primary reason bond material is lost in the sand mixing process is because the fine particles of bond material never become thoroughly wetted with water in the sand mixing process in the mullor. The inventor contemplates that such particles do not pick up sufficient added weight of water and/or are not actively bonded to the sand to effectively inhibit the particles becoming air-borne.
In any event, that bond material which is not bonded to the sand or otherwise captured as part of the mass which defines the sand mixture can readily become air-borne because the particles are sufficiently light in weight to be moved by typical air movements in the mullor. Such air-borne particles must be removed from the air stream which passes through the processing equipment, whether at sand mixing, in the sand return system, or elsewhere in the sand system, and must be captured by dust recovery apparatus and dust recovery process steps, lest such particulate matter escape into the ambient atmosphere and thereby become air-borne particulate air pollution. The dust collection sub-systems which are attached to foundry sand systems are thus designed, configured, and operated, to collect such particles.
It is an object of this invention to reduce the quantity of bond material which must be collected by dust collection apparatus in a sand system operation.
It is another object of this invention to reduce the quantity of dust which is generated in a foundry sand system, especially in the process of making sand mixes.
It is yet another object of the invention to increase the fraction of the bond material, fed into a sand mix process, which is wetted and thereby activated in the process of making foundry sand mixes.
It is still another object of the invention to reduce the amount of unactivated bond material present in the sand mix as the sand mix is being fabricated into molds for casting metal parts.
Yet another object of the invention is to provide apparatus and methods for wetting the fresh bond material being incorporated into a sand mix, such that substantially all the fresh bond material becomes wetted, and thus does not become or remain air-borne, thus avoiding generation of substantial quantities of bond material-related dust in the process of making foundry sand mixes.
It is another object of the invention to provide apparatus and methods for making foundry sand which uses less bond material than conventional processes while developing typical bond strengths.
Another object is to provide apparatus and methods for making foundry sand mixes, which sand mixes use less bond material than sand mixes made using conventional apparatus.
Still another object is to provide a process wherein at least 75 percent by weight of the bond material fed into the process ends up as actively bonding material, bonding sand particles together, in forming molds made with the resulting foundry sand mix.
A further object is to provide novel foundry sand mix compositions.
In a first family of embodiments, this invention comprehends apparatus for preparing a foundry sand mix wherein the sand mix comprises a mixture of sand and particulate bond material, for use in making sand molds to be used in casting metal parts in a foundry operation. The apparatus comprises a pre-mix tank for receiving thereinto particulate bond material and a liquid carrier therefore, and for mixing the particulate bond material and liquid carrier such as water to thereby make a slurry thereof, the pre-mix tank having a first feed port for receiving the particulate bond material into the pre-mix tank, a second separate and distinct feed port for receiving the liquid carrier into the pre-mix tank, and a discharge port for discharging the slurry from the pre-mix tank, the pre-mix tank further comprising mixing apparatus for mixing the particulate bond material and the liquid carrier to thus form the slurry; a mixer for receiving thereinto sand, liquid carrier, and particulate bond material, and for producing therefrom foundry sand mixes which can be satisfactorily bonded together by such particulate bond material so as to be operable for making foundry sand molds; and a slurry feed line for receiving the slurry from the pre-mix tank and feeding the slurry to the mixer at a feed port in the mixer.
In preferred embodiments, the apparatus includes a water feed line feeding into the slurry feed line upstream of the feed port in the mixer.
Further to preferred embodiments, the apparatus includes water spray apparatus associated with the second feed port in the pre-mix tank, the water spray apparatus being designed, configured, and positioned to apply a disperse spray of water onto a stream of bond material particles traversing an open space in the pre-mix tank.
The apparatus preferably includes a pre-mix controller for controlling quantities and timing of addition of water and bond material to the pre-mix tank.
Preferred apparatus includes a bond material hopper, and a conveyor for conveying particulate bond material from the hopper to the first feed port in the pre-mix tank.
Preferred embodiments include a water line feeding the water spray apparatus in association with the second feed port in the pre-mix tank.
Preferably, a water meter is used on the water feed line for metering desired quantities of water to the water spray apparatus such as a spray nozzle.
Preferred embodiments include a slurry pump for pumping a slurry of water and bond material from the pre-mix tank to the mixer.
In some embodiments, the mixer comprises both the feed port as a slurry entrance port for receiving slurry feed from the pre-mix tank into the mixer, and a separate and distinct fresh water entrance port for receiving fresh water into the mixer.
The slurry feed line can feed into a water feed line, and through the water feed line, into the mixer at the feed port.
In a second family of embodiments, the invention comprehends apparatus for preparing a foundry sand mix comprising a mixture of sand and particulate bond material, for use in making sand molds to be used in casting metal parts in a foundry operation. The apparatus comprises a foundry mix tank for receiving thereinto a stream of particulate bond material at a first feed port in the foundry mix tank, and expressed across an open space in the foundry mix tank; a particulate bond material feed line associated with the foundry mix tank at the first feed port, for conveying particulate foundry sand bond material to the foundry mix tank; a water feed line entering the foundry mix tank, the water feed line expressing a particulate stream of water onto such stream of particulate bond material as such stream of particulate bond material is expressed across the open space in the foundry mix tank; and a discharge port in the foundry mix tank for discharging a mixed mass of the sand, bond material, and water from the foundry mix tank.
In some embodiments, the foundry mix tank comprises a foundry sand mullor.
In other embodiments, the foundry mix tank comprises a pre-mix tank for making a slurry of water and particulate bond material, the apparatus further comprising a foundry sand mullor, and a slurry feed line for receiving slurry from the pre-mix tank and feeding the slurry to the mullor at an entrance port therefore in the mullor.
The apparatus preferably includes a pre-mix controller for controlling quantities and timing of addition of water and bond material to the pre-mix tank.
In a third family of embodiments, the invention comprehends apparatus for preparing foundry sand mixes. Such foundry sand mixes comprise mixtures of sand and particulate bond material, for use in making sand molds to be used in casting metal parts in a foundry operation. The apparatus comprises a pre-mix tank; conveying apparatus for conveying particulate bond material to the pre-mix tank using non-gaseous conveyance, and for discharging such particulate bond material into the pre-mix tank; water supply apparatus for adding water to the pre-mix tank; mixing apparatus for mixing the particulate bond material and water in the pre-mix tank to thereby make a pre-mix bond slurry; optionally a mullor for receiving the slurry made in the pre-mix tank; and optionally a discharge line for conveying the pre-mix slurry from the pre-mix tank to such mullor.
In a fourth family of embodiments, the invention comprehends a method of preparing a foundry sand mix comprising a mixture of sand and particulate bond material thus to make a foundry sand mix suitable for use in making sand molds to be used in casting metal parts in a foundry operation. The method comprises conveying particulate bond material to a pre-mix tank using non-gaseous conveyance, and discharging the particulate bond material into the pre-mix tank; adding water to the pre-mix tank; mixing the particulate bond material and water in the pre-mix tank to thereby make a pre-mix bond slurry; adding sand to the pre-mix tank in an amount of zero up to an amount which, after the recited mixing in the pre-mix tank, results in no more than 15 percent by weight of the bond material being free bond material in the pre-mix bond slurry being discharged from the pre-mix tank; optionally conveying the pre-mix bond slurry in a discharge line to a mullor; and optionally mixing the pre-mix bond slurry with sand in the mullor to thereby make the foundry sand mix suitable for use in making sand molds to be used in casting metal parts in a foundry operation.
In some embodiments, the method includes adding no substantial quantity of sand to the pre-mix tank.
In preferred embodiments, the method includes causing the particulate bond material to traverse a path across an open space in the pre-mix tank, and spraying water onto the stream of bond material particles so as to wet the bond material particles, without deleteriously deflecting the bond material particles from the path.
In some embodiments, the method includes specifying the absolute quantities of water and bond material to be mixed in the pre-mix tank according to test results obtained from at least one of (i) a recent batch of sand mix discharged from the mullor and (ii) return sand being fed to the mullor.
The method preferably includes feeding the slurry directly into the mullor through a dedicated slurry feed line.
Some methods include feeding the slurry through a slurry feed line to a water feed line, optionally diluting the slurry with water in the water feed line, and feeding the resulting slurry into the mullor through the water feed line.
In a fifth family of embodiments, the invention comprehends a method of preparing a mixture of sand and particulate bond material thus to make a foundry sand mix suitable for use in making sand molds to be used in casting metal parts in a foundry operation. The method comprises adding particulate bond material to a pre-mix tank; adding, to the pre-mix tank, water substantially free from the particulate bond material; mixing the particulate bond material and water in the pre-mix tank to thereby make a pre-mix bond slurry; and adding sand to the pre-mix tank in an amount of zero up to an amount which, after the recited mixing in the pre-mix tank, results in no more than 15 percent by weight of the bond material being free bond material in the pre-mix bond slurry; optionally conveying the pre-mix bond slurry from the pre-mix tank into a mullor; and optionally mixing the pre-mix bond slurry with sand in the mullor to thereby make the foundry sand mix suitable for use in making sand molds to be used in casting metal parts in a foundry operation.
In preferred embodiments, the method includes adding no substantial quantity of sand to the pre-mix tank.
In a sixth family of embodiments, the invention comprehends a method of preparing a mixture of sand and particulate bond material thus to make a foundry sand mix suitable for use in making sand molds to be used in casting metal parts in a foundry operation. The method comprises adding a first quantity of particulate bond material having a first set of bond properties and physical properties, to a pre-mix tank; adding a second quantity of water to the pre-mix tank; mixing the particulate bond material and water in the pre-mix tank to thereby make a pre-mix bond slurry; conveying the pre-mix bond slurry from the pre-mix tank to a mixer; adding sand, having a second set of bonding properties and physical properties, to the pre-mix tank in an amount of zero up to an amount which, after the recited mixing in the pre-mix tank, results in no more than 15 percent by weight of the bond material being free bond material in the pre-mix bond slurry, which slurry is being conveyed to the mixer; and mixing the pre-mix bond slurry with sand in the mixer to thereby make the foundry sand mix suitable for use in making the molds to be used in casting metal parts in a foundry operation. The resulting foundry sand mix has a capability to develop a given level of bond strength in making such sand molds while using, in the foundry sand mix, a quantity of bond material corresponding to the first quantity of particulate bond material of at least 5 percent less by weight than is needed to develop the respective level of bond strength, using corresponding sand and bond material, when adding the bond material and water, separately, directly to the mixer.
In a seventh family of embodiments, the invention comprehends a method of preparing a mixture of sand and bond particulate material thus to make a foundry sand mix suitable for use in making sand molds to be used in casting metal parts in a foundry operation. The method comprises adding a first quantity of fresh particulate bond material to a pre-mix tank; adding a second quantity of water to the pre-mix tank; mixing the fresh particulate bond material and water in the pre-mix tank to thereby make a pre-mix bond slurry; conveying the pre-mix bond slurry from the pre-mix tank to a mixer; adding sand, and optionally used bond material, to the pre-mix tank in an amount of zero up to an amount which, after the recited mixing in the pre-mix tank, results in no more than 15 percent by weight of the bond material being free bond material in the pre-mix bond slurry, which slurry is being conveyed to the mixer; and mixing the pre-mix bond slurry with sand, and optionally used bond material, in the mixer to thereby make the foundry sand mix suitable for use in making the molds to be used in casting metal parts in a foundry operation. The quantity of particulate bond material in the so fabricated foundry sand mix represents a quantity of bond material corresponding to at least 75 percent of the first quantity of fresh particulate bond material added to the pre-mix tank.
In an eighth family of embodiments, the invention comprehends a method of reducing the fraction of active particulate bond material in dust collected from a foundry sand system, the foundry sand system containing sand, and particulate bond material. The method comprises adding particulate bond material to a pre-mix tank; adding water to the pre-mix tank; mixing the particulate bond material and water in the pre-mix tank thus to wet substantially all of the bond material with the water and to thereby form a pre-mix bond slurry wherein substantially all of the particles of bond material are active for bonding together particles of sand; discharging the pre-mix bond slurry from the pre-mix tank to a mixer; mixing the pre-mix bond slurry with sand, including with a charge of return sand mix, for example in the mixer, wherein substantially all of the bond material in the return sand mix was initially mixed with water in the pre-mix tank, to thereby make a foundry sand molding mix; and collecting air-borne dust generated in the above recited actions, including collecting air-borne particles of bond material, less than 15 percent by weight, preferably less than 10 percent by weight, of such collected dust representing active such particulate bond material.
In a ninth family of embodiments, the invention comprehends a method of reducing the fraction of inactive bond material in foundry sand molds. The method comprises adding particulate bond material to a pre-mix tank; adding water to the pre-mix tank; mixing the particulate bond material and water in the pre-mix tank thus to wet substantially all of the bond material with the water and to thereby form a pre-mix bond slurry wherein substantially all of the particles of bond material are active for bonding together particles of sand; discharging the pre-mix bond slurry from the pre-mix tank to a mixer; mixing the pre-mix bond slurry with sand, including with a charge of return sand mix, in the mixer, wherein substantially all of the bond material in the return sand mix was initially mixed with water in the pre-mix tank, to thereby make a foundry sand molding mix; and making sand molds with the sand mix so made, the fraction of the free bond material in the resulting sand molds being no greater than 15 percent by weight of the total quantity of bond material in the sand mix.
In a tenth family of embodiments, the invention comprehends a foundry sand mix. The foundry sand mix, comprises sand, particulate bond material, and water. The sand mix includes a return sand fraction having a first set of material specifications and a fresh sand fraction having a second set of material specifications. The return sand fraction comprises return sand particles and return bond material particles. The fresh sand fraction comprises fresh sand particles and fresh bond material particles. The combination of the return sand fraction and the fresh sand fraction, when mixed together at a given ratio of fresh sand to return sand, in an environment wherein the fresh sand particles and the fresh bond particles, in combination, comprise no more than 5 percent by weight water when introduced to the mix process, and wherein the fraction of fresh bond material to fresh sand particles is a base quantity by weight, and wherein the fresh bond particles are added directly to a sand composition containing no more than 3 percent by weight water, having potential to develop a first level of green sand strength when used to make a sand mold for use in foundry operations. The sand mixes of the invention, using a return sand fraction having substantially the first set of material specifications and a fresh sand fraction having substantially the second set of material specifications, have potential, when mixed together at the given ratio, to develop the first level of green sand strength with no more than 95 percent by weight, optionally no more than 90 percent by weight, of the base quantity of fresh bond material particles in the fresh sand fraction.